Block copolymers composed of different polymer block species bound to each other are generally produced by polymerizing different monomer species in succession. Heretofore, various methods of polymerization have been developed and attempts have been made to produce block copolymers using them. When cationic polymerization is employed, however, it is difficult to control the polymerization, since the growing species carbenium ion is unstable. In recent years, examples of the so-called living cation polymerization in which the growing carbenium ion in the cationic polymerization is inhibited from undergoing isomerization, chain transfer reaction or termination reaction have been reported. For example, Higashimura et al. (Macromolecules, 17, 265, 1984) report that cationic living polymerization is possible in vinyl ether polymerization using a combination of hydrogen iodide and iodine as an initiator. However, the polymerization using such initiator has various problems; for instance, its application is restricted to those monomers which have an alkoxy group high in electron donating ability and are highly susceptible to cationic polymerization, and the initiator is unstable and difficult to handle.
On the other hand, Kennedy et al. (Japanese Kokai Publication Sho-62-48704, Japanese Kokai Publication Sho-64-62308), by polymerizing olefin monomers, such as isobutylene, using an organic carboxylic acid or an ester, or an ether as an initiator in combination with a Lewis acid, showed that cationic living polymerization is possible with olefin monomers as well. This method has been modified in several ways, and Nippon Zeon (Japanese Kokoku Publication Hei-07-59601) has succeeded in obtaining block copolymers by successive monomer addition with additional use of an amine. In this modification, isobutylene-based block copolymers comprising an isobutylene polymer and a styrene polymer are produced in an mixed solvent composed of methylene chloride and hexane. However, such halogenated hydrocarbons containing 1 or 2 carbon atoms have problems; for instance, they are difficult to handle, and require large scale equipment for preventing them from being discharged into the environment to raise the cost of production. Although, on the other hand, such polymerization is also possible in a halogen-free solvent such as toluene, very fine adjustment is required, depending on the monomer, for the monomer to show adequate polarity. It is thus very difficult to establish the conditions for successive polymerization of two or more monomer species differing in reactivity,
Furthermore, in recent years, controlled radical polymerization techniques and, further, living radical polymerization techniques have been developed, making it possible to well control the living polymerization. Matyjaszewski et al. report a method of synthesizing block copolymers by successively adding monomers using the atom transfer radical polymerization technique to be mentioned later herein or by using a macro-initiator (e.g. Macromolecules, 28, 7901, 1995). These techniques, however, may sometimes encounter problems; successive polymerization of monomers is difficult since respective monomers require different optimum polymerization conditions, or it is difficult to introduce, terminally into the macro-initiator, an initiator terminus optimal to the next monomer to be polymerized.
A further method available for the production of block copolymers comprises synthesizing respective polymer blocks individually and then coupling them to each other. In that case, however, it is not easy to accomplish the coupling reaction quantitatively and selectively. Thus, very few methods have been found that are commercially advantageous.